doc-src/Tutorial/Misc/Fib.thy

- Datatype package now also supports arbitrarily branching datatypes
(using function types).
- Added new simplification procedure for proving distinctness of
constructors.
- dtK is now a reference.

Fib = WF_Rel +
consts fib  :: nat => nat
recdef fib "measure(%n. n)"
    "fib 0 = 0"
    "fib 1 = 1"
    "fib (Suc(Suc x)) = fib x + fib (Suc x)"
end